Harvesting the onion at the correct moment is crucial for maximizing the bulb’s flavor and ensuring its ability to store long-term. Proper timing allows the plant to naturally transition into dormancy, which concentrates the flavor and begins the process of forming a protective outer skin. If bulbs are pulled too early or too late, the resulting onion may have a shorter shelf life and be more susceptible to rot.
Identifying Readiness Cues
The primary signal that an onion is reaching maturity is “lodging,” where the green tops begin to collapse. This natural event is caused by the softening of the neck, the narrow stem just above the bulb, indicating the plant has finished diverting energy to leaf growth.
This neck softening is a sign that the transfer of carbohydrates from the leaves to the bulb has largely completed, meaning the bulb is as large as it will grow. Gardeners should stop watering the plants once the tops begin to yellow to encourage the soil to dry out, which accelerates the curing process and helps prevent soil-borne diseases like sour skin. Onions are generally ready for harvest in mid-to-late summer.
Wait until 50% to 75% of the tops have naturally fallen over before starting the harvest. Harvesting when only a few tops have fallen means the remaining bulbs are likely still actively growing. Waiting for the tops to lodge ensures the plant has sealed the neck, which is a structural barrier against moisture and infection during storage.
The Physical Harvest Process
The physical removal from the ground should occur on a dry, sunny day. The goal of the harvest is to lift the bulb without causing any bruising or tearing the protective outer layers. Any damage to the bulb’s skin or neck creates an entry point for pathogens.
Use a garden fork to gently loosen the soil around the bulbs. The fork should be inserted a few inches away from the bulb to avoid slicing the onion itself. After loosening the soil, gently lift the bulbs, shaking off any large clumps of dirt. Resist the urge to wash them or aggressively clean the roots.
Leave the roots and green tops intact immediately after lifting. These parts help the onion naturally shut down and seal the bulb for long-term preservation. If the weather is dry and no frost is expected, you may leave the pulled onions lying on the soil surface for a day or two to begin the drying process. Ensure the bulbs are not exposed to direct, scorching sun.
Curing and Preparing for Storage
Curing is a mandatory post-harvest step that prepares the onion for long-term storage by drying and tightening the outer skin layers. This process effectively seals the bulb and closes the neck, which is the most vulnerable entry point for moisture and disease. The ideal environment for curing is a warm, dry, and well-ventilated space, such as a covered porch, shed, or garage, kept out of direct sunlight.
Spread the harvested onions in a single layer on a screen or rack. The temperature should be between 75 to 80 degrees Fahrenheit, with low humidity. Curing typically takes between one to three weeks.
Curing is complete when the neck feels completely dry, withered, and papery, and the outer skin is tight and brittle. The dried roots can then be trimmed close to the bulb, and the tops cut down to about one to two inches above the bulb. Store the cured onions using mesh bags or shallow crates that allow air to circulate freely.